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<td ><a href="index.html">Qt 5.14</a></td><td >QML Coding Conventions</td></tr></table><table class="buildversion"><tr>
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<li class="level1"><a href="#qml-object-declarations">QML Object Declarations</a></li>
<li class="level1"><a href="#grouped-properties">Grouped Properties</a></li>
<li class="level1"><a href="#lists">Lists</a></li>
<li class="level1"><a href="#javascript-code">JavaScript Code</a></li>
<li class="level1"><a href="#related-information">Related Information</a></li>
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<h1 class="title">QML Coding Conventions</h1>
<span class="subtitle"></span>
<!-- $$$qml-codingconventions.html-description -->
<div class="descr"> <a name="details"></a>
<p>This document contains the QML coding conventions that we follow in our documentation and examples and recommend that others follow.</p>
<a name="qml-object-declarations"></a>
<h2 id="qml-object-declarations">QML Object Declarations</h2>
<p>Throughout our documentation and examples, <a href="../qtqml/qtqml-syntax-objectattributes.html">QML object attributes</a> are always structured in the following order:</p>
<ul>
<li>id</li>
<li>property declarations</li>
<li>signal declarations</li>
<li>JavaScript functions</li>
<li>object properties</li>
<li>child objects</li>
<li>states</li>
<li>transitions</li>
</ul>
<p>For better readability, we separate these different parts with an empty line.</p>
<p>For example, a hypothetical <i>photo</i> QML object would look like this:</p>
<pre class="qml">

  <span class="type"><a href="../qtquick/qml-qtquick-rectangle.html">Rectangle</a></span> {
      <span class="name">id</span>: <span class="name">photo</span>                                               <span class="comment">// id on the first line makes it easy to find an object</span>

      property <span class="type"><a href="../qtqml/qml-bool.html">bool</a></span> <span class="name">thumbnail</span>: <span class="number">false</span>                          <span class="comment">// property declarations</span>
      property <span class="type">alias</span> <span class="name">image</span>: <span class="name">photoImage</span>.<span class="name">source</span>

      signal <span class="type">clicked</span>                                          <span class="comment">// signal declarations</span>

      <span class="keyword">function</span> <span class="name">doSomething</span>(x)                                 <span class="comment">// javascript functions</span>
      {
          <span class="keyword">return</span> <span class="name">x</span> <span class="operator">+</span> <span class="name">photoImage</span>.<span class="name">width</span>
      }

      <span class="name">color</span>: <span class="string">&quot;gray&quot;</span>                                           <span class="comment">// object properties</span>
      <span class="name">x</span>: <span class="number">20</span>                                                   <span class="comment">// try to group related properties together</span>
      <span class="name">y</span>: <span class="number">20</span>
      <span class="name">height</span>: <span class="number">150</span>
      <span class="name">width</span>: {                                                <span class="comment">// large bindings</span>
          <span class="keyword">if</span> (<span class="name">photoImage</span>.<span class="name">width</span> <span class="operator">&gt;</span> <span class="number">200</span>) {
              <span class="name">photoImage</span>.<span class="name">width</span>;
          } <span class="keyword">else</span> {
              <span class="number">200</span>;
          }
      }

      <span class="type"><a href="../qtquick/qml-qtquick-rectangle.html">Rectangle</a></span> {                                             <span class="comment">// child objects</span>
          <span class="name">id</span>: <span class="name">border</span>
          <span class="name">anchors</span>.centerIn: <span class="name">parent</span>; <span class="name">color</span>: <span class="string">&quot;white&quot;</span>

          <span class="type"><a href="../qtquick/qml-qtquick-image.html">Image</a></span> {
              <span class="name">id</span>: <span class="name">photoImage</span>
              <span class="name">anchors</span>.centerIn: <span class="name">parent</span>
          }
      }

      <span class="name">states</span>: <span class="name">State</span> {                                         <span class="comment">// states</span>
          <span class="name">name</span>: <span class="string">&quot;selected&quot;</span>
          <span class="type"><a href="../qtquick/qml-qtquick-propertychanges.html">PropertyChanges</a></span> { <span class="name">target</span>: <span class="name">border</span>; <span class="name">color</span>: <span class="string">&quot;red&quot;</span> }
      }

      <span class="name">transitions</span>: <span class="name">Transition</span> {                               <span class="comment">// transitions</span>
          <span class="name">from</span>: <span class="string">&quot;&quot;</span>
          <span class="name">to</span>: <span class="string">&quot;selected&quot;</span>
          <span class="type"><a href="../qtquick/qml-qtquick-coloranimation.html">ColorAnimation</a></span> { <span class="name">target</span>: <span class="name">border</span>; <span class="name">duration</span>: <span class="number">200</span> }
      }
  }

</pre>
<a name="grouped-properties"></a>
<h2 id="grouped-properties">Grouped Properties</h2>
<p>If using multiple properties from a group of properties, consider using <i>group notation</i> instead of <i>dot notation</i> if it improves readability.</p>
<p>For example, this:</p>
<pre class="qml">

  <span class="type"><a href="../qtquick/qml-qtquick-rectangle.html">Rectangle</a></span> {
      <span class="name">anchors</span>.left: <span class="name">parent</span>.<span class="name">left</span>; <span class="name">anchors</span>.top: <span class="name">parent</span>.<span class="name">top</span>; <span class="name">anchors</span>.right: <span class="name">parent</span>.<span class="name">right</span>; <span class="name">anchors</span>.leftMargin: <span class="number">20</span>
  }

  <span class="type"><a href="../qtquick/qml-qtquick-text.html">Text</a></span> {
      <span class="name">text</span>: <span class="string">&quot;hello&quot;</span>
      <span class="name">font</span>.bold: <span class="number">true</span>; <span class="name">font</span>.italic: <span class="number">true</span>; <span class="name">font</span>.pixelSize: <span class="number">20</span>; <span class="name">font</span>.capitalization: <span class="name">Font</span>.<span class="name">AllUppercase</span>
  }

</pre>
<p>could be written like this:</p>
<pre class="qml">

  <span class="type"><a href="../qtquick/qml-qtquick-rectangle.html">Rectangle</a></span> {
      <span class="type">anchors</span> { <span class="name">left</span>: <span class="name">parent</span>.<span class="name">left</span>; <span class="name">top</span>: <span class="name">parent</span>.<span class="name">top</span>; <span class="name">right</span>: <span class="name">parent</span>.<span class="name">right</span>; <span class="name">leftMargin</span>: <span class="number">20</span> }
  }

  <span class="type"><a href="../qtquick/qml-qtquick-text.html">Text</a></span> {
      <span class="name">text</span>: <span class="string">&quot;hello&quot;</span>
      <span class="type"><a href="../qtquick/qml-font.html">font</a></span> { <span class="name">bold</span>: <span class="number">true</span>; <span class="name">italic</span>: <span class="number">true</span>; <span class="name">pixelSize</span>: <span class="number">20</span>; <span class="name">capitalization</span>: <span class="name">Font</span>.<span class="name">AllUppercase</span> }
  }

</pre>
<a name="lists"></a>
<h2 id="lists">Lists</h2>
<p>If a list contains only one element, we generally omit the square brackets.</p>
<p>For example, it is very common for a component to only have one state.</p>
<p>In this case, instead of:</p>
<pre class="qml">

  <span class="name">states</span>: [
      <span class="type"><a href="../qtqml/qml-qtqml-statemachine-state.html">State</a></span> {
          <span class="name">name</span>: <span class="string">&quot;open&quot;</span>
          <span class="type"><a href="../qtquick/qml-qtquick-propertychanges.html">PropertyChanges</a></span> { <span class="name">target</span>: <span class="name">container</span>; <span class="name">width</span>: <span class="number">200</span> }
      }
  ]

</pre>
<p>we will write this:</p>
<pre class="qml">

  <span class="name">states</span>: <span class="name">State</span> {
      <span class="name">name</span>: <span class="string">&quot;open&quot;</span>
      <span class="type"><a href="../qtquick/qml-qtquick-propertychanges.html">PropertyChanges</a></span> { <span class="name">target</span>: <span class="name">container</span>; <span class="name">width</span>: <span class="number">200</span> }
  }

</pre>
<a name="javascript-code"></a>
<h2 id="javascript-code">JavaScript Code</h2>
<p>If the script is a single expression, we recommend writing it inline:</p>
<pre class="qml">

  <span class="type"><a href="../qtquick/qml-qtquick-rectangle.html">Rectangle</a></span> { <span class="name">color</span>: <span class="string">&quot;blue&quot;</span>; <span class="name">width</span>: <span class="name">parent</span>.<span class="name">width</span> <span class="operator">/</span> <span class="number">3</span> }

</pre>
<p>If the script is only a couple of lines long, we generally use a block:</p>
<pre class="qml">

  <span class="type"><a href="../qtquick/qml-qtquick-rectangle.html">Rectangle</a></span> {
      <span class="name">color</span>: <span class="string">&quot;blue&quot;</span>
      <span class="name">width</span>: {
          var w = <span class="name">parent</span>.<span class="name">width</span> <span class="operator">/</span> <span class="number">3</span>
          <span class="name">console</span>.<span class="name">debug</span>(<span class="name">w</span>)
          <span class="keyword">return</span> <span class="name">w</span>
      }
  }

</pre>
<p>If the script is more than a couple of lines long or can be used by different objects, we recommend creating a function and calling it like this:</p>
<pre class="qml">

  <span class="keyword">function</span> <span class="name">calculateWidth</span>(object)
  {
      var w = <span class="name">object</span>.<span class="name">width</span> <span class="operator">/</span> <span class="number">3</span>
      <span class="comment">// ...</span>
      <span class="comment">// more javascript code</span>
      <span class="comment">// ...</span>
      <span class="name">console</span>.<span class="name">debug</span>(<span class="name">w</span>)
      <span class="keyword">return</span> <span class="name">w</span>
  }

  <span class="type"><a href="../qtquick/qml-qtquick-rectangle.html">Rectangle</a></span> { <span class="name">color</span>: <span class="string">&quot;blue&quot;</span>; <span class="name">width</span>: <span class="name">calculateWidth</span>(<span class="name">parent</span>) }

</pre>
<p>For long scripts, we will put the functions in their own JavaScript file and import it like this:</p>
<pre class="qml">

  import &quot;myscript.js&quot; as Script

  <span class="type"><a href="../qtquick/qml-qtquick-rectangle.html">Rectangle</a></span> { <span class="name">color</span>: <span class="string">&quot;blue&quot;</span>; <span class="name">width</span>: <span class="name">Script</span>.<span class="name">calculateWidth</span>(<span class="name">parent</span>) }

</pre>
<p>If the code is longer than one line and hence within a block, we use semicolons to indicate the end of each statement:</p>
<pre class="qml">

  <span class="type"><a href="../qtquick/qml-qtquick-mousearea.html">MouseArea</a></span> {
      <span class="name">anchors</span>.fill: <span class="name">parent</span>
      <span class="name">onClicked</span>: {
          var scenePos = <span class="name">mapToItem</span>(<span class="number">null</span>, <span class="name">mouseX</span>, <span class="name">mouseY</span>);
          <span class="name">console</span>.<span class="name">log</span>(<span class="string">&quot;MouseArea was clicked at scene pos &quot;</span> <span class="operator">+</span> <span class="name">scenePos</span>);
      }
  }

</pre>
<a name="related-information"></a>
<h2 id="related-information">Related Information</h2>
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<li><a href="../qtquick/qtquick-bestpractices.html">Best Practices for QML and Qt Quick</a></li>
</ul>
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